Acarina, pycnogonids, Permian ticks?
Hovenkamp at NHN.LEIDENUNIV.NL
Thu Apr 19 10:19:59 CDT 2001
At 11:46 AM 4/18/01 -0400, John R. Grehan wrote:
> From my perspective the invoking of centers of origin and dispersal events
>on nothing more than a presumption is not much better, if at all, to
>thinking. Much (perhaps most) of what passes for biogeography is simply
>dreadful. This criticism is not simply
>a matter of taking a particular approach to biogeography (whether area
>panbiogeographic, dispersalist etc), but the lack of rigor in the
>what qualifies as biogeographic evidence and the explicit rendition of what
>constitutes empirical evidence and what is read into the 'evidence' from a
>theorized position. For me it seems that the basic standards of science for
>biogeography are simply missing from the cited tick work.
>The option missing from Klompen's account is the possibility that the ticks
>were primitively cosmopolitan with respect to the range of the relevant
>taxa. Thus the ancestor
>of Carios was throughout its current range rather than origination from a
>center of origin within one part of the range. The possibility of a more
>may be applicable, but at present there is no analytical foundation for
>such an assertion.
Could it be that the foundation for such an assertion is based on:
- The assumption that in the past, the average range of a taxon was not
significantly different from what it is now (a position called actualism, I
believe), so that there must have been many local species, some of which
inevitably ancestral to current groups?
- The consideration that speciation is far easier to achieve in small
isolated populations, and therefore is far more frequent in small "centres
of origin" than is sympatric speciation occurring simultaneously over a
Thus, without any distinct evidence to the contrary, the foundation for
such an assertion may not be analytical (whatever that may be), but
nevertheless good science. Science has to start somewhere, and does not
progress if one has to argue each starting point from first principles.
Sorry if I may have missed some important defect in Klompen's reaoning, but
I do not have the zoological literature at hand.
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